1. Field of the Invention
An embodiment of the present invention relates to a light-emitting device utilizing electroluminescence. Further, an embodiment of the present invention relates to an electronic device and a lighting device which utilize the light-emitting device.
2. Description of the Related Art
In recent years, research and development have been extensively conducted on light-emitting elements using electroluminescence (hereinafter, referred to as EL). In a basic structure of such a light-emitting element, a layer containing a substance with a light-emitting property is interposed between a pair of electrodes. By applying a voltage to this element, light emission from the light-emitting substance can be obtained.
Since the above light-emitting element is a self-luminous type, a light-emitting device using this light-emitting element has advantages such as high visibility, no necessity of a backlight, low power consumption, and the like. Further, such a light-emitting element also has advantages in that the element can be formed to be thin and lightweight, and that response time is high.
For example, in the case where the light-emitting element is applied to an active matrix light-emitting device, a light-emitting element is formed over a substrate in which a transistor or the like controlling light emission is formed in some cases. With such a structure (bottom-emission structure) where light emitted from a light-emitting element is extracted to outside through a substrate in which a transistor or the like is formed, there is a problem in that an aperture ratio becomes low depending on a wiring, a transistor, or the like.
In order to solve this problem, a structure (top-emission structure) where light is extracted from the side opposite to an element substrate is proposed (see Patent Document 1, for example). By using a top-emission structure, the aperture ratio can be increased, and the extraction efficiency of light can be increased, which are advantageous to low power consumption and high definition.
In the light-emitting device, a coloring method in which light-emitting elements emitting red, green or blue light are arranged in matrix and a coloring method with a colored layer (that is, a color filter) using a light-emitting element emitting white light are used. In the case of the coloring method with a color filter, a black matrix (BM) which is a light-blocking film is provided to prevent each color from being mixed or improve contrast.
However, light from the light-emitting element provided in the light-emitting device is partially absorbed in the black matrix (BM), and the light-extraction efficiency is decreased. Electric power is required to increase the light-extraction efficiency; thus, there is a problem in that power consumption is increased.
In order to solve this problem, a display device including a solar cell with low power consumption is proposed (Patent Document 2 and Patent Document 3, for example).
[Reference]
    [Patent Document 1] Japanese Published Patent Application No. 2001-043980    [Patent Document 2] Japanese Published Patent Application No. H11-295725    [Patent Document 3] Japanese Published Patent Application No. 2008-164851